The invention relates generally to triple wall corrugated paper board and, more particularly, to a new and improved flap fold construction for such material, a process for forming the fold construction and devices used in the process.
Triple wall corrugated paper board is a lamination of four paper liners and three corrugated paper mediums, each of the mediums being interposed between two liners in each instance. The liners and mediums are intimately and rigidly secured to each other by adhesive applied to the ridges of the corrugations of the mediums.
The corrugations of the mediums are parallel to each other throughout the board. Three types of corrugations are typically used in triple wall construction, namely, types A, B and C. "A" flute is approximately 3/16 of an inch (4.7625 mm) high with 33.8 flutes of corrugations per linear foot (1.181 flutes of the corrugations per linear cm). "B" flute is approximately 1/8 of an inch (3.175 mm) high with 50 flutes of the corrugations per linear foot (1.6406 flutes of the corrugations per linear cm). "C" flute is about 5/32 of an inch (3.9688 mm) high with 42 flutes of the corrugations per linear foot (1.378 flutes of the corrugations per linear cm).
Various grades of paper board of different weight and characteristics are used for forming the corrugated medium and liner. Consequently, triple wall corrugated paper board is relatively thick and rigid. For example, triple wall corrugated paper board formed of A-A-A fluting is about 5/8 of an inch (15.875 mm) thick and, if made of A-A-C fluting, is about 9/16 of an inch (14.288 mm) thick.
Triple wall corrugated paper board has superb rigidity and strength, which compares favorably to wood as a packaging material. Yet, it is lightweight, foldable and has cushioning qualities that cannot be approached by wood. The strength, rigidity and cushioning properties of triple wall corrugated paper board makes it particularly useful and versatile in packaging a variety of articles of large volumes that may be heavy or fragile, or both. For example, cartons made of triple wall corrugated paper board are used for containing heavy materials such as industrial machinery or large appliances, smaller heavier materials such as machine parts, materials that are shiftable in transit such as bulk flowables, bulky agricultural products such as large loads of melons, and fragile items that may not necessarily be heavy as well, such as electronic equipment.
Triple wall corrugated paper board has been successfully manufactured for many years in accordance with the general techniques described in U.S. Pat. Nos. 2,759,523 and 3,290,205.
Foldable cartons composed of triple wall corrugated paper board are ordinarily made from flat blanks that are scored and slotted to define the side panels and end flaps of the cartons. When such a carton is assembled, the panels and end flaps are folded along the score lines. Because of the rigidity and thickness of the triple wall corrugated paper board, resistance is often experienced in folding the flaps, especially in the case of cartons having narrow flaps. One expedient employed to reduce this difficulty has been the formation of a broad score line to crush the flap in the bending zone and, thereby, to minimize bending resistance. This solution is not entirely satisfactory, however, because the bending line is not clearly defined and the flap may tend to bend unevenly and unpredictably.
Another solution proposed for minimizing the resistance to bending of the flap, described in U.S. Pat. No. 3,122,976, is the provision of a blank with a crush-relieved zone contiguous to the score lines for the flaps. Nevertheless, when such a bend is made in triple wall corrugated paper board, a substantial amount of paper is compressed into the corner of the bend. This may cause the flap adjacent to the bend to bow slightly and prevent the flap from resting on a plane surface. The resulting carton, therefore, may rock. In addition, large forces may be required to bend the flap.
One solution, particularly for extra-long folds such as use needed for folding the panels in long-tubular containers, has been to cut a V-shaped groove into the board only through two of the corrugated mediums and two liners leaving the third "wall" composed of a corrugated medium, two liners undamaged so that sufficient material remains to preserve the integrity of the board. On the other hand, sufficient material is removed by the cutter so that the remaining paper, when compressed into the score does not cause the flap to bow and the flap remains flat. The force required to bend the board is considerately reduced. Great care must be exercised, however, in order to precisely remove the adhesively-bonded liners and fluting without damage to the remaining material.
An alternative solution has been the formation of triple wall corrugated paper board sheet having single wall flaps. In this construction, two single face webs of the triple wall lamination have a shorter width than the third single face web and fourth liner. The small band along the edge of the shorter intermediate single face web is not glued to the underlying longer liner of the single face web bonded to the fourth liner. The edge is scored, slit and trimmed. A single wall flap is thereby formed. The single wall flap is easily foldable. A number of difficulties, however, have been experienced. In the formation process, in the heating section of the corrugated paper board machine, it is difficult to secure proper adhesion along the single wall flap due to the differences in the thickness relative to the remainder of the board. In addition, the resulting board is difficult to fabricate into boxes, the board stacks unevenly and is more difficult to print. The single wall flaps are not as sturdy as triple wall flaps.
Thus, a need exists for a flap fold construction for triple wall corrugated paper board which does not have the disadvantages of various prior constructions but is simple to manufacture and stable in construction.